How to get task manager back if it is disabled?

Hello friends,
I am having a serious problem in my PC. I use windows XP service pack 3. It’s about 3 months ago when I setup that OS. It was quite well till last night. But, today am getting too much problems with my operating system.
It became too much slower than past. The task manager window is not running. I use ctrl+ alt+ delete to call task manager. These keys are not working. When I try to call task manager by right clicking on the taskbar, it is looking as it is disabled. But I didn’t make it disabled. I don’t know why it has been disabled by itself. While operating the pc, I use the task manager for several times. It is very important for me to get the task manager okay.
I wrote “gpedit.msc” on the run menu to call group policy window. I tried many settings there, but it was not showing. Is there any other way to get it back without reinstalling the operating system? Please, anybody help me to get my task manager back on my PC.
Thank you all.
